The present invention relates to a field conversion method of producing field data having a new field number from field data having an arbitrary field number during nonstandard speed play of a freeze picture (still picture) or the like by a magnetic video recording and reproducing apparatus (hereinafter referred to as "VTR" for short, when applicable) or the like, and an apparatus employing the same.
When a video signal recorded by VTR or the like is reproduced, for the adjustment of a regenerative time, or slow playback, fast playback, freeze picture playback or the like for providing a special effect, a picture may be suitably thinned out or the same picture may be repeatedly displayed in some cases. At this time, a video signal of which a field number is different from that of a regenerative video signal needs to be produced so as to fulfill the interlace conditions of the video signal and the conditions of continuity of the color subcarrier, i.e., in order to maintain continuity of four field numbers of a four-field sequence in the case of the NTSC television signal. In order to attain the production of that video signal, the degradation of the vertical resolution of an image during the special playback is often reduced using the technology of an interpolation filter. Examples of such an interpolation filter unit are shown in (1) JP-A-2-132984 and (2) U.S. Pat. No. 4,641,202.
Moreover, the processing technology in the case where the above processing is performed by a digital VTR is shown in (3) "Reproduced Video Signal Processing for Composite Digital VTR", ITEJ Technical Report, Vol. 14, No. 47, pp. 13-18.
Further, one example of a motion detection circuit of a field conversion circuit for processing a video signal between the fields to perform the interpolation is shown in (4) JP-A-3-13790.
As shown in the above articles (1), (2) and (3), in those systems, the vertical movement of the picture image occurs along with the field conversion. The vertical movement of the picture image produces a visual anxiety feeling and degrades remarkably the picture quality. In the case where the freeze picture is outputted, only the signals of one field are used. Therefore, there arises a problem in that the vertical resolution is degraded and as a result the edge of the picture image corrugates.
Moreover, in the above-mentioned prior art, there is a possibility that the regenerative signal skips and the above-mentioned motion detection circuit and the field conversion circuit fall into malfunction because the migration period up to the servo locking and the state in the abnormality of the servo in the VTR is not taken into consideration at all.